The invention relates to a method for measuring an angularly resolved intensity distribution in a reticle plane of a projection exposure apparatus for microlithography, and to a projection exposure apparatus comprising a measurement system for measuring an angularly resolved intensity distribution. Furthermore, the invention relates to a method for measuring a beam divergence in an illumination system of a projection exposure apparatus for microlithography, and to a projection exposure apparatus.
Lenses of projection exposure apparatuses for microlithography are being operated with ever smaller k1 factors. This has the consequence that a precise measurement and specification of the illumination system of such projection exposure apparatuses is becoming more and more important. Such an illumination system irradiates a reticle to be imaged with a previously selected angular distribution. The angular distribution chosen is also designated as an illumination setting. Examples of such illumination settings include annular illumination, dipole illumination and quadrupole illumination. In particular, it is important to be able to characterize the illumination setting even when the projection lens and the illumination system are integrated in a projection exposure apparatus.
The illumination setting in a projection exposure apparatus is conventionally characterized by measuring a so-called “pupilogram” with a sensor integrated in the wafer stage of the projection exposure apparatus. A definition of a pupilogram is included e.g. in the article by Joe Kirk and Christopher Progler “Pinholes and pupil fills”, Microlithography World, Autumn 1997, pages 25 to 34. In order to generate the pupilogram, a special measurement reticle with pinhole structures arranged thereon is loaded into the reticle plane of the projection exposure apparatus. The above-mentioned sensor is generally arranged for measurement purposes below the wafer plane, to be precise in a conjugate pupil plane of the projection lens. This has the effect that the intensity distribution which is present in the pupil plane and which corresponds to the angularly resolved intensity distribution in the reticle plane is imaged on the sensor.
If this method is used during the projection operation of the projection exposure apparatus, then generally a relatively significant time delay arises since firstly the production reticle has to be removed from the wafer stage and the pinhole reticle has to be loaded for carrying out the measurement. Furthermore, in the case of generally older projection exposure apparatuses, the problem often arises that such apparatuses are not provided with a suitable sensor arranged below the wafer plane for carrying out the pupilogram measurement.